Various proposals about electrically conductive fibers have conventionally been made. For example, an electrically conductive fiber obtained by plating metal onto the surface of a fiber having no electrical conductivity is known. However, there is a problem with such an electrically conductive fiber having a metal plating layer on its surface that the electrically conducting performance is degraded because the plating layer on the surface readily exfoliates during a knitting/weaving process or its following process or the plating layer is readily dissolved and removed during a dyeing treatment or a refining treatment of textile.
Metal fiber is known as another type of electrically conductive fiber. It, however, has problems that metal fiber is high in cost and poor in spinnability. Further, it causes troubles during the knitting/weaving process or dye-finishing process, it readily breaks or exfoliates in washing during wearing, and it readily gathers rust.
In place of such known technologies using metal, an electrically conductive composite fiber is known which is obtained by adding electrically conductive carbon black to a polymer, causing the resultant to exist in the form of an electrically conductive layer on the surface of or inside a fiber continuously along the longitudinal direction of the fiber, and composite spinning the resultant with another fiber-forming polymer. It, however, has the following problem: in order to obtain electrically conducting performance by using a polymer to which electrically conductive carbon black has been added (hereinafter, referred to as an electrically conductive layer), a large amount of electrically conductive carbon black must be added to the polymer, whereas if a large amount of carbon black is added, the spinnability and stretchability of the polymer are degraded abruptly. As a method for solving problems caused by stretching, a method including no stretching is conceivable. However, when stretching is not performed, the fiber itself has a low strength and the carbon black in the electrically conductive layer fails to form the structure described infra, and therefore no satisfactory electrically conducting performance will be obtained. Moreover, such a method has a drawback that if the stretching is performed by force, the electrically conductive layer will be broken in the fiber or, even if it is not broken, the structure of the electrically conductive carbon black will be broken or the electrically conductive layer will be broken readily when a slight external force is applied to the electrically conductive fiber, and as a result the electrically conducting performance will be lost.
There is another problem that an electrically conductive layer containing large amount of carbon black shows a low adhesiveness to another polymer constituting the fiber and, as a result, interfacial peeling will occur readily during a process for producing woven/knitted fabrics or during the use as an electrically conductive product to change the electrically conductive layer to a sole fiber and an electrically conductive layer with a low strength and elongation at break will be broken easily (see, for example, patent documents 1, 2).
Furthermore, electrically conductive fibers have been used in dust-proof clothing in order to prevent fine dust from adhering to clothing due to static electricity. In conventional electrically conductive fibers, polyamide-based resins, to which a large amount of electrically conductive carbon black can be added, have been used as a resin for electrically conductive layers. The site of semiconductor manufacture is a typical example of the industry where persons work while wearing dust-proof clothing. The manufacture of semiconductors includes a step of washing a semiconductor or its raw material with acid. Dust-proof clothing used in such a workplace is required to have acid resistance. Generally, however, when the resin used in electrically conductive fibers is a polyamide-based resin, there is a problem that the electrically conductive fibers using the polyamide-based resin can not be used in dust-proof clothing because polyamide resin is poor in acid resistance. Moreover, there are many dust-proof sites where acid may be used or contacted other than the sites of semiconductor manufacture. Therefore, sale of dust-proof clothing which can not be used in workplaces where acid is used is limited greatly.
Patent document 1: JP 57-29611 A
Patent document 2: JP 58-132119 A